JPH023272Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] The present invention is a spark plug for use in miniaturized spark ignition internal combustion engines required in recent internal combustion engine-driven two-wheeled vehicles and four-wheeled vehicles. , relates to a spark plug with a small outer diameter of the external thread of the mounting screw portion. Hereinafter, the spark ignition internal combustion engine will be simply referred to as engine.

[Conventional technology]

The recent trend in engines is to make them smaller, but at the same time demand higher performance in order to achieve higher output.
For this reason, while the engine head itself is becoming smaller, there are demands for larger outer diameters of intake and exhaust valves and an increase in the number of valves, which reduces the degree of freedom in determining the placement of spark plugs. However, the space available for installation is also becoming tighter. Furthermore, in such a high-performance engine, the wall thickness is thicker than the strength required for the engine cylinder and engine head, so the reach L is increased as shown for the conventional spark plug shown in Figure 2. A large long reach type spark plug is required.

On the other hand, from the perspective of the spark plug itself, due to the dimensional requirements of the engine head mentioned above, the reach L of the male thread of the spark plug mounting thread increases as described above.
A small external thread diameter is required.

The following description will be made with reference to the accompanying drawings, in which identical or similar components will be designated by the same reference numerals.

A conventional spark plug manufactured based on the above requirements is shown in FIG. In Figure 2,
Reference number 1 is the mounting housing, 1a is the threaded part of the mounting housing, 2 is the insulator, 2a is the insulator leg,
2b is the insulator middle part, 2c is the insulator body, 3 is the center electrode, 3f is the flange of the center electrode 3, 4 is the heat conductive packing, 5 is the resistor for preventing radio noise, 6 is the ground electrode, 11 is the Gasket shown. As can be seen from Fig. 2, in the conventional long reach type spark plug with a small external diameter of the external thread, the mounting housing threaded part 1a and the insulator middle part 2b have a long straight shape, and the center electrode 3 also has a long straight shape. long, and
The flange 3f is located inside the insulator body 2c, and is located away from the packing 4. Note that 11 in the figure is a gasket.

The conventional spark plug with the above structure has a long threaded portion 1a, which is not only inconvenient to attach and remove, but also has poor strength and is distorted when tightened, making the airtightness between the threaded portion 1a and the insulator 2 difficult. In addition, the insulator 2 has the drawbacks of easily becoming distorted during firing, which reduces productivity. Therefore, efforts have been made to eliminate these drawbacks, and prior art materials showing examples of such efforts are as follows: For example, there is Japanese Patent Application Laid-Open No. 60-28191 (Japanese Patent Application No. 136223-1982).

The improved spark plug disclosed by the above-mentioned prior art document has an outer shape similar to the spark plug shown in FIG. In the spark plug shown in FIG. 1, the threaded portion 1a of the mounting housing 1 of the spark plug shown in FIG. Side length L _a
It has an outer shape consisting of two parts: a mounting threaded part 1a, and an unthreaded cylindrical part 1b having an outer diameter larger than the outer diameter of the external thread and having a length L _b . Thereby, the drawbacks of the conventional spark plug, such as the inconvenience of attaching and detaching it and the deterioration of the strength of the threaded portion 1a, can be avoided.

[Problem that the invention attempts to solve]

Conventional spark plugs have various drawbacks, such as the above-mentioned inconvenience in attaching and detaching, deterioration in the strength of the threaded portion 1a, and the like, as described below.

(1) The temperature of the center electrode 32 increases significantly, and its wear is severe.

(2) Poor pre-ignition resistance.

(3) Resistor-containing spark plugs (resistor plugs) have poor radio noise prevention characteristics because the resistor 5 is installed at a distance from the spark gap.

(4) The middle part 2b of the insulator 2 has an elongated shape,
Furthermore, the long length of the center electrode 3 is disadvantageous in manufacturing.

The present invention was devised in view of the above-mentioned problems, and the object thereof is to provide a spark plug for a spark-ignited internal combustion engine that has a simple structure and solves the above-mentioned problems that could not be solved with conventional technology. shall be.

[Means for solving problems]

In the spark plug according to the present invention, as shown in FIG. 1, the mounting portion (length L) of the mounting housing 1 has a mounting screw portion 1a (length L _a ) provided on the side of the spark gap; Adjacent thereto, there is a cylindrical portion 1b (length L _b ) having an outer diameter larger than the outer diameter of the male thread, but which is not threaded. In addition, the insulator 2 is engaged with a protruding step provided on the inner wall of the center hole of the mounting screw portion 1a of the mounting housing 1 via the heat conductive packing 4 at the outer lower end of the middle lower part 2b, The outer diameter of the middle upper part 2b' and the inner diameter of the center through hole are made larger corresponding to the cylindrical portions 1b of the mounting housing 1 facing each other. Furthermore, the flange 3f of the center electrode 3
is configured to engage with a shoulder on the inner wall of the central through hole located at the lower part of the middle insulator upper part 2b'.

[Effect]

In the spark plug according to the present invention, the length of the center electrode 3 is shortened, and the gasket 4 whose flange 3f forms a dissipation path for heat conducted inside the center electrode 3
The close arrangement facilitates the dissipation of heat flow through the center electrode 3, reducing its temperature. Further, by shortening the length of the center electrode 3, in the case of a resistor-containing spark plug, the position of the resistor 5 can be brought closer to the spark gap.

〔Example〕

FIG. 1 shows a cross section of a main part of a spark plug for a spark-ignition internal combustion engine according to the present invention. In Fig. 1, 1 is a metal mounting housing for mounting a spark plug on an engine head, and in its center hole is an insulator 2, which is further fitted into the center through-hole of the insulator 2. Center electrode 3, conductive glass layer 9 on top of it, resistor 5 on top of it, conductive glass layer 8 on top of it, and terminal member 7 arranged on top of it.
It includes.

The spark plug according to the present invention described above is fitted into the mounting hole of the engine head with the gasket 11 interposed, similar to the long reach flat sheet type spark plug disclosed in the prior art document mentioned above. Length L of mounting housing 1
The mounting part is provided on the side of the spark gap, and the length is
L _a , and a mounting threaded portion 1a having a mounting male thread with an outer diameter D, and an adjacent mounting thread portion 1a with an outer diameter D of the male thread.
It consists of a cylindrical part 1b which has a larger outer diameter and a length L _b and is not externally threaded. Further, a protruding stepped portion is provided on the inner wall of the central hole of the mounting portion at a portion corresponding to the mounting screw portion 1a.

The insulator 2 includes an insulator head 2h, an insulator body 2c having the largest outer diameter, an insulator middle upper part 2b' facing the lower mounting housing cylindrical portion 1b, and a lower mounting housing mounting. It includes an insulator middle lower part 2b facing the threaded part 1a and an insulator leg part 2a further below. The insulator 2 has a stepped portion at the boundary between the middle lower portion 2b and the leg portion 2a, with a packing 4 interposed therebetween, and a protruding stepped portion on the inner wall of the center hole of the mounting screw portion 1a of the mounting housing 1. It is firmly held inside the mounting housing 1 by engaging and caulking the ring-shaped edge of the upper end of the mounting housing 1 against the upper shoulder of the body 2c. In addition, the middle upper part 2 of the insulator 2
The outer diameter of b' and the inner diameter of its central through hole are made larger in accordance with the outer diameter and inner diameter of the opposing cylindrical portion 1b of the mounting housing 1.

In the center electrode 3, the flange 3f at the end opposite to the spark gap engages with a shoulder provided on the inner wall of the center through hole at the lower part of the middle insulator upper part 2b',
It is then pressed and supported by the terminal member 7 via the conductive glass layers 8 and 9 and the resistor 5 which are fitted into the central through hole above.

An example of the dimensions of the spark plug according to the embodiment of the present invention configured as described above is as follows:
The external diameter of the male thread of the mounting thread part 1a of the mounting part D = 10
mm, length of the mounting part L = 19mm, length of the mounting screw part 1a L _a = 12.7mm, length of the cylindrical part 1b L _b = 6.3mm
Further, the length from the flange of the center electrode 3 to the tip of the other end is 18 mm.

In the configuration of the spark plug of the present invention described above, the length of the center electrode 3 is shorter than that of the spark plug according to the prior art, and the position of the flange 3f is set to a gasket that forms a heat dissipation path. 4 and gasket 11.

Next, various characteristics obtained as a result of a test in which the spark plug of the present invention having the above configuration was installed in an engine and operated, and characteristics obtained as a result of a radio noise test will be explained.

FIG. 3 shows the results of a spark plug electrode wear test conducted on the spark plugs of the present invention and the prior art by 100 hours of bench operation using the same engine. According to it, 4 under the same conditions
As a result of comparing the amount of increase in the spark gap, which indicates the amount of electrode wear after 100 hours of operation of a 125 cc cycle engine, the amount of electrode wear of the spark plug of the present invention was reduced by about 25% than that of the spark plug of the prior art.

Next, Fig. 4 shows the results of a preignition resistance test using the same 4-cycle 125cc engine.

In this pre-ignition test, the pre-ignition temperature of the test spark plug of the present invention and the spark plug of the prior art was measured using a high-temperature measuring thermocouple placed inside the tip of the center electrode. corresponds to the indicated temperature of the spark plug.
That is, by advancing the ignition timing of the engine, the temperature of the spark plug is increased, and the advance angle at which the test spark plug starts to cause pre-ignition (pre-ignition) is determined. By determining the relationship between spark plug temperature and ignition advance angle, the pre-ignition temperatures (°C) of the test plugs were compared.

According to the results, the temperature at which pre-ignition occurs increased by approximately 40°C in the spark plug of the present invention compared to the spark plug of the prior art.

Furthermore, FIG. 5A shows the arrangement of the spark plug under test and the measuring device when a comparison test was conducted on the level of radio noise generated during operation between the spark plug of the present invention and the spark plug of the prior art. It shows the status of. Furthermore, FIG. 5B shows comparative measurement results of the level of radio noise generated by the test spark plug when a test was conducted using the measurement arrangement of FIG. 5A.

In this case, the measurement of radio noise generated by the test spark plug should be conducted in order to avoid the influence of noise radio waves emitted from parts other than the spark plug, such as the ignition coil, high voltage cable, and other ignition device parts.
A measurement arrangement as shown in Figure 5A was used. The test plugs, the spark plug of the present invention and the spark plug of the prior art, both had a built-in resistor for radio noise prevention with a resistance value of 5KΩ. Also,
The test spark plug was placed in an air pressure environment of 4 atmospheres, simulating the case where it was installed in an engine head, and the spark generation frequency was set to correspond to an engine rotation speed of 2.000 rpm. A radio noise pickup coil was placed, and its detection output signal was guided to the input terminal of the radio noise measuring instrument. In addition, as the measured value of the level of generated radio wave noise, the maximum value among several measured values was adopted. Under the above measurement conditions, the results of a comparative measurement of the distribution of the level of radio noise generated by the spark plug of the present invention and the spark plug of the prior art with respect to the radio noise frequency band are shown in FIG. 5B. According to it, 90~
Measurement results showed that the level of radio noise generated by the spark plug of the present invention was lower by about 2 dB in the 180 MHz frequency band and by about 3 dB in the 300-800 MHz frequency band.

FIG. 6 shows an example of a practical state in which the spark plug of the present invention is installed in an engine head. The dashed line drawn from the center electrode of the spark plug through the wall of the engine head indicates that the flow of heat transferred from the combustion gases of the engine to the center electrode of the spark plug of the present invention is directed through the wall of the engine head. This diagram schematically shows the route taken when dissipating through the .

〔Effect of the invention〕

As clearly understood from the above explanation,
In the spark plug for a spark-ignited internal combustion engine according to the present invention, the inner and outer diameters of the middle upper part of the insulator facing the cylindrical part with increased inner and outer diameters and no external threads of the mounting part of the mounting housing are increased; By arranging the flange of the center electrode so as to engage with the shoulder on the inner wall of the center through-hole with an inner diameter of Since it can be placed close to the center electrode, it can provide favorable conditions for the dissipation of heat transferred from the combustion gas inside the engine head to the center electrode, and at the same time it can provide favorable conditions for the dissipation of heat transferred from the combustion gas inside the engine head to the center electrode. The distance between the resistor and the spark gap can be shortened.

As a result, as is clear from the results of the various comparative tests described above, the spark plug of the present invention has: (1) reduced electrode wear compared to spark plugs of the prior art; It has a long lifespan.

(2) The pre-ignition temperature becomes higher and the usable operating (temperature) range becomes wider.

(3) Better radio noise prevention effects can be obtained.

It can produce excellent effects such as:

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part of a spark plug according to the present invention. FIG. 2 is a sectional view of a main part of a conventional spark plug. FIG. 3 is a comparison chart showing the results of the electrode wear test. FIG. 4 is a comparison diagram showing the results of a preignition resistance test. 5th A
The figure is a measurement layout diagram schematically showing the arrangement of a test spark plug and a measurement device for a radio noise test. FIG. 5B is a comparison diagram showing the radio noise test results. FIG. 6 is a partial sectional view showing a practical state in which the spark plug according to the present invention is installed in an engine. Explanation of symbols, 1...Mounting housing, 1a...
Mounting screw part of the mounting part of the mounting housing, 1b...
...Cylindrical part of the mounting part of the mounting housing, 2...Insulator, 2a...Insulator leg, 2b...Insulator middle lower part, 2b'...Insulator middle upper part, 2c...Insulator trunk, 2h ... Insulator head, 3 ... Center electrode, 3
f... Center electrode flange, 4... Packing, 5... Resistor, 6... Ground electrode, 7... Terminal member, 8, 9
... Conductive glass layer, 10 ... Caulking ring, 1
1...Gasket.

Claims (1)

[Scope of utility model registration request] In a spark plug for a spark-ignited internal combustion engine, a center electrode with a flange at the end opposite to the tip that forms the spark gap is fitted into a center through hole, and an insulator is held inside the center hole. The mounting part of the housing, which is fitted into the wall of a cylinder head of an internal combustion engine, has a cylindrical part and a male screw having an outer diameter smaller than the outer diameter of the cylindrical part on the outer wall, In the spark plug for an internal combustion engine, the mounting housing includes a mounting screw portion having a protruding step on the inner wall of the hole, and the insulator includes a middle upper portion corresponding to the cylindrical portion and a mounting screw portion. Corresponding parts include a lower middle stage having an outer diameter smaller than the outer diameter of the upper middle stage and leg parts having an outer diameter even smaller than the outer diameter of the lower middle stage,
The outer lower end of the middle lower portion engages with the inner wall protruding step of the mounting screw portion of the mounting housing via a heat conductive packing, and further, the center electrode has a collar portion that is connected to the middle step of the insulator. A spark plug for a spark-ignition internal combustion engine having a configuration in which the spark plug is supported by engaging with a shoulder on an inner wall of the center through hole located at a lower portion of the upper portion.